Fabrication of electronic circuit elements using liquid deposition techniques is of profound interest as such techniques provide potentially low-cost alternatives to conventional mainstream amorphous silicon technologies for electronic applications such as thin film transistors (TFTs), light-emitting diodes (LEDs), RFID tags, photovoltaics, etc. However, the deposition and/or patterning of functional electrodes, pixel pads, and conductive traces, lines and tracks which meet the conductivity, processing and cost requirements for practical applications have been a great challenge. Silver is of particular interest as conductive elements for electronic devices because silver is much lower in cost than gold and it possesses much better environmental stability than copper. There is therefore a void, addressed by embodiments herein, for lower cost methods for preparing liquid processable, stable silver compositions that are suitable for fabricating electrically conductive elements of electronic devices.
Solution-processable conductors are of great interest for printed electronic applications as electrodes, conducting lines in thin film transistors, RFID tags, photovoltaics, etc. Silver nanoparticle-based conductive inks represent a promising class of materials for printed electronics. However, most silver nanoparticles necessitate large molecular weight stabilizers to ensure proper solubility and stability in forming a printable solution. These large molecular weight stabilizers inevitably raise the annealing temperature for the silver nanoparticles above 200° C. in order to remove the stabilizers, which temperatures are incompatible with most plastic substrates and can cause damage or deformation thereto.
Further, the use of lower molecular weight stabilizers can also be problematic, as smaller size stabilizers often do not provide desired solubility and often fail to effectively prevent coalescence or aggregation of the silver nanoparticles before use. Therefore, the use of organoamines as stabilizers provides the desired solubility while allowing coalescence or aggregation of the silver nanoparticles.
Prior lab-scale methods for producing silver nanoparticles used multiple steps and were laborious and time-consuming. The results were not reproducible or easily scaled up for large-scale manufacturing. In addition, the resultant product typically manifested as a sticky paste, raising handling issues. The final product also had a short shelf life and low purity.
There is therefore a need, addressed by embodiments of the present disclosure, for lower cost methods for preparing large-scale amounts of liquid processable, stable silver-containing nanoparticle compositions that are suitable for fabricating electrically conductive elements of electronic devices.